Storage system architecture for striping data container content across volumes of a cluster

ABSTRACT

A storage system architecture comprises one or more volumes distributed across a plurality of nodes interconnected as a cluster. The volumes are organized as a striped volume set (SVS) and configured to store content of data containers served by the cluster in response to multi-protocol data access requests issued by clients. Each node of the cluster includes (i) a storage server adapted to service a volume of the SVS and (ii) a multi-protocol engine adapted to redirect the data access requests to any storage server of the cluster. Notably, the content of each data container is apportioned among the volumes of the SVS to thereby improve the efficiency of storage service provided by the cluster.

This application is a Continuation-in-Part application of U.S. patentapplication Ser. No. 10/727,169, entitled METHOD AND APPARATUS FOR DATASTORAGE USING STRIPING, by Michael L. Kazar, et al, filed on Dec. 2,2003, the contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to storage systems and, in particularto striping a file across a plurality of volumes on one or more storagesystems.

BACKGROUND OF THE INVENTION

A storage system typically comprises one or more storage devices intowhich information may be entered, and from which information may beobtained, as desired. The storage system includes a storage operatingsystem that functionally organizes the system by, inter alia, invokingstorage operations in support of a storage service implemented by thesystem. The storage system may be implemented in accordance with avariety of storage architectures including, but not limited to, anetwork-attached storage environment, a storage area network and a diskassembly directly attached to a client or host computer. The storagedevices are typically disk drives organized as a disk array, wherein theterm “disk” commonly describes a self-contained rotating magnetic mediastorage device. The term disk in this context is synonymous with harddisk drive (HDD) or direct access storage device (DASD).

The storage operating system of the storage system may implement ahigh-level module, such as a file system, to logically organize theinformation stored on volumes as a hierarchical structure of datacontainers, such as files and logical units. For example, each “on-disk”file may be implemented as set of data structures, i.e., disk blocks,configured to store information, such as the actual data for the file.These data blocks are organized within a volume block number (vbn) spacethat is maintained by the file system. The file system may also assigneach data block in the file a corresponding “file offset” or file blocknumber (fbn). The file system typically assigns sequences of fbns on aper-file basis, whereas vbns are assigned over a larger volume addressspace. The file system organizes the data blocks within the vbn space asa “logical volume”; each logical volume may be, although is notnecessarily, associated with its own file system.

A known type of file system is a write-anywhere file system that doesnot over-write data on disks. If a data block is retrieved (read) fromdisk into a memory of the storage system and “dirtied” (i.e., updated ormodified) with new data, the data block is thereafter stored (written)to a new location on disk to optimize write performance. Awrite-anywhere file system may initially assume an optimal layout suchthat the data is substantially contiguously arranged on disks. Theoptimal disk layout results in efficient access operations, particularlyfor sequential read operations, directed to the disks. An example of awrite-anywhere file system that is configured to operate on a storagesystem is the Write Anywhere File Layout (WAFL™) file system availablefrom Network Appliance, Inc., Sunnyvale, Calif.

The storage system may be further configured to operate according to aclient/server model of information delivery to thereby allow manyclients to access data containers stored on the system. In this model,the client may comprise an application, such as a database application,executing on a computer that “connects” to the storage system over acomputer network, such as a point-to-point link, shared local areanetwork (LAN), wide area network (WAN), or virtual private network (VPN)implemented over a public network such as the Internet. Each client mayrequest the services of the storage system by issuing file-based andblock-based protocol messages (in the form of packets) to the systemover the network.

A plurality of storage systems may be interconnected to provide astorage system environment configured to service many clients. Eachstorage system may be configured to service one or more volumes, whereineach volume stores one or more data containers. Yet often a large numberof data access requests issued by the clients may be directed to a smallnumber of data containers serviced by a particular storage system of theenvironment. A solution to such a problem is to distribute the volumesserviced by the particular storage system among all of the storagesystems of the environment. This, in turn, distributes the data accessrequests, along with the processing resources needed to service suchrequests, among all of the storage systems, thereby reducing theindividual processing load on each storage system. However, a noteddisadvantage arises when only a single data container, such as a file,is heavily accessed by clients of the storage system environment. As aresult, the storage system attempting to service the requests directedto that data container may exceed its processing resources and becomeoverburdened, with a concomitant degradation of speed and performance.

SUMMARY OF THE INVENTION

The present invention overcomes the disadvantages of the prior art byproviding a storage system architecture comprising one or more volumesdistributed across a plurality of nodes interconnected as a cluster. Thevolumes are organized as a striped volume set (SVS) and configured tostore content of data containers, such as files and logical units,served by the cluster in response to multi-protocol data access requestsissued by clients. Each node of the cluster includes (i) a storageserver adapted to service a volume of the SVS and (ii) a multi-protocolengine adapted to redirect the data access requests to any storageserver of the cluster. Notably, the content of each data container isapportioned among the volumes of the SVS to thereby improve theefficiency of storage service provided by the cluster.

According to an aspect of the invention, the SVS comprises one meta-datavolume (MDV), and one or more data volumes (DV). The MDV is configuredto store a canonical copy of meta-data, including access control listsand directories, associated with all data containers stored on the SVS,whereas each DV is configured to store, at least, data content of thosecontainers. For each data container stored on the SVS, one volume isdesignated the CAV and, to that end, is configured to store (“cache”)certain, rapidly-changing attribute meta-data associated with thatcontainer to thereby offload access requests that would otherwise bedirected to the MDV.

According to another aspect of the invention, the SVS is associated witha set of striping rules that define a stripe algorithm, a stripe widthand an ordered list of volumes within the SVS. The stripe algorithmspecifies the manner in which data container content is apportioned asstripes across the plurality of volumes, while the stripe widthspecifies the size/width of each stripe. Moreover, the ordered list ofvolumes may specify the function and implementation of the variousvolumes and striping rules of the SVS. For example, the first volume inthe ordered list may denote the MDV of the SVS, whereas the ordering ofvolumes in the list may denote the manner of implementing a particularstriping algorithm, e.g., round-robin.

In the illustrative embodiment, the storage server of each node isembodied as a disk element (D-blade) and the multi-protocol engine isembodied as a network element (N-blade). The N-blade receives amulti-protocol data access request from a client, converts that requestinto a cluster fabric (CF) message and redirects the message to anappropriate D-blade of the cluster. A CF module of the N-Bladeimplements a novel Locate( ) function to compute the location of datacontainer content in the SVS volume to which the message is directed tothereby ensure consistency of such content served by the cluster. EachD-blade comprises a file system and a volume striping module (VSM) thatcooperate to service a volume of the SVS by processing the CF message inaccordance with the striping rules. In particular, the VSM implementsthe novel Locate( ) function.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of invention may be better understoodby referring to the following description in conjunction with theaccompanying drawings in which like reference numerals indicateidentical or functionally similar elements:

FIG. 1 is a schematic block diagram of a plurality of nodesinterconnected as a cluster in accordance with an embodiment of thepresent invention;

FIG. 2 is a schematic block diagram of a node in accordance with anembodiment of the present invention;

FIG. 3 is a schematic block diagram of a storage operating system thatmay be advantageously used with the present invention;

FIG. 4 is a schematic block diagram illustrating the format of a clusterfabric (CF) message in accordance with an embodiment of with the presentinvention;

FIG. 5 is a schematic block diagram illustrating the format of a datacontainer handle in accordance with an embodiment of the presentinvention;

FIG. 6 is a schematic block diagram of an exemplary inode in accordancewith an embodiment of the present invention;

FIG. 7 is a schematic block diagram of an exemplary buffer tree inaccordance with an embodiment of the present invention;

FIG. 8 is a schematic block diagram of an illustrative embodiment of abuffer tree of a file that may be advantageously used with the presentinvention;

FIG. 9 is a schematic block diagram of an exemplary aggregate inaccordance with an embodiment of the present invention;

FIG. 10 is a schematic block diagram of an exemplary on-disk layout ofthe aggregate in accordance with an embodiment of the present invention;

FIG. 11 is a schematic block diagram illustrating a collection ofmanagement processes in accordance with an embodiment of the presentinvention;

FIG. 12 is a schematic block diagram of a volume location database(VLDB) volume entry in accordance with an embodiment of the presentinvention;

FIG. 13 is a schematic block diagram of a VLDB aggregate entry inaccordance with an embodiment of the present invention;

FIG. 14 is a schematic block diagram of a striped volume set (SVS) inaccordance with an embodiment of the present invention;

FIG. 15 is a schematic block diagram of a VLDB SVS entry in accordancewith an embodiment the present invention;

FIG. 16 is a schematic block diagram illustrating the periodicsparseness of file content stored on volumes of a SVS in accordance withan embodiment of the present invention;

FIG. 17 is a flowchart detailing steps of a procedure for creating a newfile in accordance with an embodiment of the present invention;

FIG. 18 is a flowchart detailing the steps of a procedure for deleting afile in accordance with embodiment of the present invention;

FIG. 18 is a flowchart detailing the steps of a procedure for retrievingattributes of a file in accordance with an embodiment of the presentinvention;

FIG. 20 is a flowchart detailing the steps of a procedure forwriting/modifying file attributes in accordance with an embodiment ofthe present invention;

FIG. 21 is a flowchart detailing the steps of a procedure for processinga read request in accordance with an embodiment of the presentinvention; and

FIG. 22 is a flowchart detailing the steps of a procedure for processinga write request in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

A. Cluster Environment

FIG. 1 is a schematic block diagram of a plurality of nodes 200interconnected as a cluster 100 and configured to provide storageservice relating to the organization of information on storage devices.The nodes 200 comprise various functional components that cooperate toprovide a distributed storage system architecture of the cluster 100. Tothat end, each node 200 is generally organized as a network element(N-blade 310) and a disk element (D-blade 350). The N-blade 310 includesfunctionality that enables the node 200 to connect to clients 180 over acomputer network 140, while each D-blade 350 connects to one or morestorage devices, such as disks 130 of a disk array 120. The nodes 200are interconnected by a cluster switching fabric 150 which, in theillustrative embodiment, may be embodied as a Gigabit Ethernet switch.An exemplary distributed file system architecture is generally describedin U.S. patent application Publication No. US 2002/0116593 titled METHODAND SYSTEM FOR RESPONDING TO FILE SYSTEM REQUESTS, by M. Kazar et al.published Aug. 22, 2002. It should be noted that while there is shown anequal number of N and D-blades in the illustrative cluster 100, theremay be differing numbers of N and/or D-blades in accordance with variousembodiments of the present invention. For example, there may be aplurality of N-blades and/or D-blades interconnected in a clusterconfiguration 100 that does not reflect a one-to-one correspondencebetween the N and D-blades. As such, the description of a node 200comprising one N-blade and one D-blade should be taken as illustrativeonly.

The clients 180 may be general-purpose computers configured to interactwith the node 200 in accordance with a client/server model ofinformation delivery. That is, each client may request the services ofthe node, and the node may return the results of the services requestedby the client, by exchanging packets over the network 140. The clientmay issue packets including file-based access protocols, such as theCommon Internet File System (CIFS) protocol or Network File System (NFS)protocol, over the Transmission Control Protocol/Internet Protocol(TCP/IP) when accessing information in the form of files anddirectories. Alternatively, the client may issue packets includingblock-based access protocols, such as the Small Computer SystemsInterface (SCSI) protocol encapsulated over TCP (iSCSI) and SCSIencapsulated over Fibre Channel (FCP), when accessing information in theform of blocks.

B. Storage System Node

FIG. 2 is a schematic block diagram of a node 200 that is illustrativelyembodied as a storage system comprising a plurality of processors222a,b, a memory 224, a network adapter 225, a cluster access adapter226, a storage adapter 228 and local storage 230 interconnected by asystem bus 223. The local storage 230 comprises one or more storagedevices, such as disks, utilized by the node to locally storeconfiguration information (e.g., in configuration table 235) provided byone or more management processes that execute as user mode applications1100 (see FIG. 11). The cluster access adapter 226 comprises a pluralityof ports adapted to couple the node 200 to other nodes of the cluster100. In the illustrative embodiment, Ethernet is used as the clusteringprotocol and interconnect media, although it will be apparent to thoseskilled in the art that other types of protocols and interconnects maybe utilized within the cluster architecture described herein. Inalternate embodiments where the N-blades and D-blades are implemented onseparate storage systems or computers, the cluster access adapter 226 isutilized by the N/D-blade for communicating with other N/D-blades in thecluster 100.

Each node 200 is illustratively embodied as a dual processor storagesystem executing a storage operating system 300 that preferablyimplements a high-level module, such as a file system, to logicallyorganize the information as a hierarchical structure of nameddirectories, files and special types of files called virtual disks(hereinafter generally “blocks”) on the disks. However, it will beapparent to those of ordinary skill in the art that the node 200 mayalternatively comprise a single or more than two processor system.Illustratively, one processor 222 a executes the functions of theN-blade 310 on the node, while the other processor 222 b executes thefunctions of the D-blade 350.

The memory 224 illustratively comprises storage locations that areaddressable by the processors and adapters for storing software programcode and data structures associated with the present invention. Theprocessor and adapters may, in turn, comprise processing elements and/orlogic circuitry configured to execute the software code and manipulatethe data structures. The storage operating system 300, portions of whichis typically resident in memory and executed by the processing elements,functionally organizes the node 200 by, inter alia, invoking storageoperations in support of the storage service implemented by the node. Itwill be apparent to those skilled in the art that other processing andmemory means, including various computer readable media, may be used forstoring and executing program instructions pertaining to the inventiondescribed herein.

The network adapter 225 comprises a plurality of ports adapted to couplethe node 200 to one or more clients 180 over point-to-point links, widearea networks, virtual private networks implemented over a publicnetwork (Internet) or a shared local area network. The network adapter225 thus may comprise the mechanical, electrical and signaling circuitryneeded to connect the node to the network. Illustratively, the computernetwork 140 may be embodied as an Ethernet network or a Fibre Channel(FC) network. Each client 180 may communicate with the node over network140 by exchanging discrete frames or packets of data according topre-defined protocols, such as TCP/IP.

The storage adapter 228 cooperates with the storage operating system 300executing on the node 200 to access information requested by theclients. The information may be stored on any type of attached array ofwritable storage device media such as video tape, optical, DVD, magnetictape, bubble memory, electronic random access memory, micro-electromechanical and any other similar media adapted to store information,including data and parity information. However, as illustrativelydescribed herein, the information is preferably stored on the disks 130of array 120. The storage adapter comprises a plurality of ports havinginput/output (I/O) interface circuitry that couples to the disks over anI/O interconnect arrangement, such as a conventional high-performance,FC link topology.

Storage of information on each array 120 is preferably implemented asone or more storage “volumes” that comprise a collection of physicalstorage disks 130 cooperating to define an overall logical arrangementof volume block number (vbn) space on the volume(s). Each logical volumeis generally, although not necessarily, associated with its own filesystem. The disks within a logical volume/file system are typicallyorganized as one or more groups, wherein each group may be operated as aRedundant Array of Independent (or Inexpensive) Disks (RAID). Most RAIDimplementations, such as a RAID-4 level implementation, enhance thereliability/integrity of data storage through the redundant writing ofdata “stripes” across a given number of physical disks in the RAIDgroup, and the appropriate storing of parity information with respect tothe striped data. An illustrative example of a RAID implementation is aRAID-4 level implementation, although it should be understood that othertypes and levels of RAID implementations may be used in accordance withthe inventive principles described herein.

C. Storage Operating System

To facilitate access to the disks 130, the storage operating system 300implements a write-anywhere file system that cooperates with one or morevirtualization modules to “virtualize” the storage space provided bydisks 130. The file system logically organizes the information as ahierarchical structure of named directories and files on the disks. Each“on-disk” file may be implemented as set of disk blocks configured tostore information, such as data, whereas the directory may beimplemented as a specially formatted file in which names and links toother files and directories are stored. The virtualization module(s)allow the file system to further logically organize information as ahierarchical structure of blocks on the disks that are exported as namedlogical unit numbers (luns).

In the illustrative embodiment, the storage operating system ispreferably the NetApp® Data ONTAP™ operating system available fromNetwork Appliance, Inc., Sunnyvale, Calif. that implements a WriteAnywhere File Layout (WAFL™) file system. However, it is expresslycontemplated that any appropriate storage operating system may beenhanced for use in accordance with the inventive principles describedherein. As such, where the term “WAFL” is employed, it should be takenbroadly to refer to any storage operating system that is otherwiseadaptable to the teachings of this invention.

FIG. 3 is a schematic block diagram of the storage operating system 300that may be advantageously used with the present invention. The storageoperating system comprises a series of software layers organized to forman integrated network protocol stack or, more generally, amulti-protocol engine 325 that provides data paths for clients to accessinformation stored on the node using block and file access protocols.The multi-protocol engine includes a media access layer 312 of networkdrivers (e.g., gigabit Ethernet drivers) that interfaces to networkprotocol layers, such as the IP layer 314 and its supporting transportmechanisms, the TCP layer 316 and the User Datagram Protocol (UDP) layer315. A file system protocol layer provides multi-protocol file accessand, to that end, includes support for the Direct Access File System(DAFS) protocol 318, the NFS protocol 320, the CIFS protocol 322 and theHypertext Transfer Protocol (HTTP) protocol 324. A VI layer 326implements the VI architecture to provide direct access transport (DAT)capabilities, such as RDMA, as required by the DAFS protocol 318. AniSCSI driver layer 328 provides block protocol access over the TCP/IPnetwork protocol layers, while a FC driver layer 330 receives andtransmits block access requests and responses to and from the node. TheFC and iSCSI drivers provide FC-specific and iSCSI-specific accesscontrol to the blocks and, thus, manage exports of luns to either iSCSIor FCP or, alternatively, to both iSCSI and FCP when accessing theblocks on the node 200.

In addition, the storage operating system includes a series of softwarelayers organized to form a storage server 365 that provides data pathsfor accessing information stored on the disks 130 of the node 200. Tothat end, the storage server 365 includes a file system module 360 incooperating relation with a volume striping module (VSM) 370, a RAIDsystem module 380 and a disk driver system module 390. The RAID system380 manages the storage and retrieval of information to and from thevolumes/disks in accordance with I/O operations, while the disk driversystem 390 implements a disk access protocol such as, e.g., the SCSIprotocol. The VSM 370 illustratively implements a striped volume set(SVS) of the present invention. As described further herein, the VSMcooperates with the file system 360 to enable storage server 365 toservice a volume of the SVS. In particular, the VSM 370 implements thenovel Locate( ) function 375 to compute the location of data containercontent in the SVS volume to thereby ensure consistency of such contentserved by the cluster.

The file system 360 implements a virtualization system of the storageoperating system 300 through the interaction with one or morevirtualization modules illustratively embodied as, e.g., a virtual disk(vdisk) module (not shown) and a SCSI target module 335. The vdiskmodule enables access by administrative interfaces, such as a userinterface of a management framework 1110 (see FIG. 11), in response to auser (system administrator) issuing commands to the node 200. The SCSItarget module 335 is generally disposed between the FC and iSCSI drivers328, 330 and the file system 360 to provide a translation layer of thevirtualization system between the block (lun) space and the file systemspace, where luns are represented as blocks.

The file system 360 is illustratively a message-based system thatprovides logical volume management capabilities for use in access to theinformation stored on the storage devices, such as disks. That is, inaddition to providing file system semantics, the file system 360provides functions normally associated with a volume manager. Thesefunctions include (i) aggregation of the disks, (ii) aggregation ofstorage bandwidth of the disks, and (iii) reliability guarantees, suchas mirroring and/or parity (RAID). The file system 360 illustrativelyimplements the WAFL file system (hereinafter generally the“write-anywhere file system”) having an on-disk format representationthat is block-based using, e.g., 4 kilobyte (kB) blocks and using indexnodes (“inodes”) to identify files and file attributes (such as creationtime, access permissions, size and block location). The file system usesfiles to store meta-data describing the layout of its file system; thesemeta-data files include, among others, an inode file. A file handle,i.e., an identifier that includes an inode number, is used to retrievean inode from disk.

Broadly stated, all inodes of the write-anywhere file system areorganized into the inode file. A file system (fs) info block specifiesthe layout of information in the file system and includes an inode of afile that includes all other inodes of the file system. Each logicalvolume (file system) has an fsinfo block that is preferably stored at afixed location within, e.g., a RAID group. The inode of the inode filemay directly reference (point to) data blocks of the inode file or mayreference indirect blocks of the inode file that, in turn, referencedata blocks of the inode file. Within each data block of the inode fileare embedded inodes, each of which may reference indirect blocks that,in turn, reference data blocks of a file.

Operationally, a request from the client 180 is forwarded as a packetover the computer network 140 and onto the node 200 where it is receivedat the network adapter 225. A network driver (of layer 312 or layer 330)processes the packet and, if appropriate, passes it on to a networkprotocol and file access layer for additional processing prior toforwarding to the write-anywhere file system 360. Here, the file systemgenerates operations to load (retrieve) the requested data from disk 130if it is not resident “in core”, i.e., in memory 224. If the informationis not in memory, the file system 360 indexes into the inode file usingthe inode number to access an appropriate entry and retrieve a logicalvbn. The file system then passes a message structure including thelogical vbn to the RAID system 380; the logical vbn is mapped to a diskidentifier and disk block number (disk,dbn) and sent to an appropriatedriver (e.g., SCSI) of the disk driver system 390. The disk driveraccesses the dbn from the specified disk 130 and loads the requesteddata block(s) in memory for processing by the node. Upon completion ofthe request, the node (and operating system) returns a reply to theclient 180 over the network 140.

It should be noted that the software “path” through the storageoperating system layers described above needed to perform data storageaccess for the client request received at the node may alternatively beimplemented in hardware. That is, in an alternate embodiment of theinvention, a storage access request data path may be implemented aslogic circuitry embodied within a field programmable gate array (FPGA)or an application specific integrated circuit (ASIC). This type ofhardware implementation increases the performance of the storage serviceprovided by node 200 in response to a request issued by client 180.Moreover, in another alternate embodiment of the invention, theprocessing elements of adapters 225, 228 may be configured to offloadsome or all of the packet processing and storage access operations,respectively, from processor 222, to thereby increase the performance ofthe storage service provided by the node. It is expressly contemplatedthat the various processes, architectures and procedures describedherein can be implemented in hardware, firmware or software.

As used herein, the term “storage operating system” generally refers tothe computer-executable code operable on a computer to perform a storagefunction that manages data access and may, in the case of a node 200,implement data access semantics of a general purpose operating system.The storage operating system can also be implemented as a microkernel,an application program operating over a general-purpose operatingsystem, such as UNIX® or Windows NT®, or as a general-purpose operatingsystem with configurable functionality, which is configured for storageapplications as described herein.

In addition, it will be understood to those skilled in the art that theinvention described herein may apply to any type of special-purpose(e.g., file server, filer or storage serving appliance) orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings of this invention can be adapted to a variety of storagesystem architectures including, but not limited to, a network-attachedstorage environment, a storage area network and disk assemblydirectly-attached to a client or host computer. The term “storagesystem” should therefore be taken broadly to include such arrangementsin addition to any subsystems configured to perform a storage functionand associated with other equipment or systems. It should be noted thatwhile this description is written in terms of a write any where filesystem, the teachings of the present invention may be utilized with anysuitable file system, including a write in place file system.

D. CF Protocol

In the illustrative embodiment, the storage server 365 is embodied asD-blade 350 of the storage operating system 300 to service one or morevolumes of array 120. In addition, the multi-protocol engine 325 isembodied as N-blade 310 to (i) perform protocol termination with respectto a client issuing incoming data access request packets over thenetwork 140, as well as (ii) redirect those data access requests to anystorage server 365 of the cluster 100. Moreover, the N-blade 310 andD-blade 350 cooperate to provide a highly-scalable, distributed storagesystem architecture of the cluster 100. To that end, each blade includesa cluster fabric (CF) interface module 340 a,b adapted to implementintra-cluster communication among the blades, includingD-blade-to-D-blade communication for data container striping operationsdescribed herein.

The protocol layers, e.g., the NFS/CIFS layers and the iSCSI/FC layers,of the N-blade 310 function as protocol servers that translatefile-based and block based data access requests from clients into CFprotocol messages used for communication with the D-blade 350. That is,the N-blade servers convert the incoming data access requests into filesystem primitive operations (commands) that are embedded within CFmessages by the CF interface module 340 for transmission to the D-blades350 of the cluster 100. Notably, the CF interface modules 340 cooperateto provide a single file system image across all D-blades 350 in thecluster 100. Thus, any network port of an N-blade that receives a clientrequest can access any data container within the single file systemimage located on any D-blade 350 of the cluster.

Further to the illustrative embodiment, the N-blade 310 and D-blade 350are implemented as separately-scheduled processes of storage operatingsystem 300; however, in an alternate embodiment, the blades may beimplemented as pieces of code within a single operating system process.Communication between an N-blade and D-blade is thus illustrativelyeffected through the use of message passing between the blades although,in the case of remote communication between an N-blade and D-blade ofdifferent nodes, such message passing occurs over the cluster switchingfabric 150. A known message-passing mechanism provided by the storageoperating system to transfer information between blades (processes) isthe Inter Process Communication (IPC) mechanism. The protocol used withthe IPC mechanism is illustratively a generic file and/or block-based“agnostic” CF protocol that comprises a collection of methods/functionsconstituting a CF application programming interface (API). Examples ofsuch an agnostic protocol are the SpinFS and SpinNP protocols availablefrom Network Appliance, Inc. The SpinFS protocol is described in theabove-referenced U.S. patent application Publication No. US2002/0116593.

The CF interface module 340 implements the CF protocol for communicatingfile system commands among the blades of cluster 100. Communication isillustratively effected by the D-blade exposing the CF API to which anN-blade (or another D-blade) issues calls. To that end, the CF interfacemodule 340 is organized as a CF encoder and CF decoder. The CF encoderof, e.g., CF interface 340 a on N-blade 310 encapsulates a CF message as(i) a local procedure call (LPC) when communicating a file systemcommand to a D-blade 350 residing on the same node 200 or (ii) a remoteprocedure call (RPC) when communicating the command to a D-bladeresiding on a remote node of the cluster 100. In either case, the CFdecoder of CF interface 340 b on D-blade 350 de-encapsulates the CFmessage and processes the file system command.

FIG. 4 is a schematic block diagram illustrating the format of a CFmessage 400 in accordance with an embodiment of with the presentinvention. The CF message 400 is illustratively used for RPCcommunication over the switching fabric 150 between remote blades of thecluster 100; however, it should be understood that the term “CF message”may be used generally to refer to LPC and RPC communication betweenblades of the cluster. The CF message 400 includes a media access layer402, an IP layer 404, a UDP layer 406, a reliable connection (RC) layer408 and a CF protocol layer 410. As noted, the CF protocol is a genericfile system protocol that conveys file system commands related tooperations contained within client requests to access data containersstored on the cluster 100; the CF protocol layer 410 is that portion ofmessage 400 that carries the file system commands. Illustratively, theCF protocol is datagram based and, as such, involves transmission ofmessages or “envelopes” in a reliable manner from a source (e.g., anN-blade 310) to a destination (e.g., a D-blade 350). The RC layer 408implements a reliable transport protocol that is adapted to process suchenvelopes in accordance with a connectionless protocol, such as UDP 406.

A data container, e.g., a file, is accessed in the file system using adata container handle. FIG. 5 is a schematic block diagram illustratingthe format of a data container handle 500 including a SVS ID field 502,an inode number field 504, a unique-ifier field 506 a striped flag field508 and a striping epoch number field 510. The SVS ID field 502 containsa global identifier (within the cluster 100) of the SVS within which thedata container resides. The inode number field 504 contains an inodenumber of an inode (within an inode file) pertaining to the datacontainer. The unique-ifier field 506 contains a monotonicallyincreasing number that uniquely identifies the data container handle500. The unique-ifier is particularly useful in the case where an inodenumber has been deleted, reused and reassigned to a new data container.The unique-ifier distinguishes that reused inode number in a particulardata container from a potentially previous use of those fields. Thestriped flag field 508 is illustratively a Boolean value that identifieswhether the data container is striped or not. The striping epoch numberfield 510 indicates the appropriate striping technique for use with thisdata container for embodiments where the SVS utilizes differing stripingtechniques for different data containers.

E. File System Organization

In the illustrative embodiment, a data container is represented in thewrite-anywhere file system as an inode data structure adapted forstorage on the disks 130. FIG. 6 is a schematic block diagram of aninode 600, which preferably includes a meta-data section 605 and a datasection 660. The information stored in the meta-data section 605 of eachinode 600 describes the data container (e.g., a file) and, as such,includes the type (e.g., regular, directory, vdisk) 610 of file, itssize 615, time stamps (e.g., access and/or modification time) 620 andownership, i.e., user identifier (UID 625) and group ID (GID 630), ofthe file. The meta-data section 605 also includes a generation number631, and a meta-data invalidation flag field 634. As described furtherherein, meta-data invalidation flag field 634 is used to indicatewhether meta-data in this inode is usable or whether it should bere-acquired from the MDV. The contents of the data section 660 of eachinode may be interpreted differently depending upon the type of file(inode) defined within the type field 610. For example, the data section660 of a directory inode contains meta-data controlled by the filesystem, whereas the data section of a regular inode contains file systemdata. In this latter case, the data section 660 includes arepresentation of the data associated with the file.

Specifically, the data section 660 of a regular on-disk inode mayinclude file system data or pointers, the latter referencing 4kB datablocks on disk used to store the file system data. Each pointer ispreferably a logical vbn to facilitate efficiency among the file systemand the RAID system 380 when accessing the data on disks. Given therestricted size (e.g., 128 bytes) of the inode, file system data havinga size that is less than or equal to 64 bytes is represented, in itsentirety, within the data section of that inode. However, if the lengthof the contents of the data container exceeds 64 bytes but less than orequal to 64 kB, then the data section of the inode (e.g., a first levelinode) comprises up to 16 pointers, each of which references a 4 kBblock of data on the disk.

Moreover, if the size of the data is greater than 64 kB but less than orequal to 64 megabytes (MB), then each pointer in the data section 660 ofthe inode (e.g., a second level inode) references an indirect block(e.g., a first level L1 block) that contains 1024 pointers, each ofwhich references a 4 kB data block on disk. For file system data havinga size greater than 64 MB, each pointer in the data section 660 of theinode (e.g., a third level L3 inode) references a double-indirect block(e.g., a second level L2 block) that contains 1024 pointers, eachreferencing an indirect (e.g., a first level L1) block. The indirectblock, in turn, that contains 1024 pointers, each of which references a4 kB data block on disk. When accessing a file, each block of the filemay be loaded from disk 130 into the memory 224.

When an on-disk inode (or block) is loaded from disk 130 into memory224, its corresponding in-core structure embeds the on-disk structure.For example, the dotted line surrounding the inode 600 indicates thein-core representation of the on-disk inode structure. The in-corestructure is a block of memory that stores the on-disk structure plusadditional information needed to manage data in the memory (but not ondisk). The additional information may include, e.g., a “dirty” bit 670.After data in the inode (or block) is updated/modified as instructed by,e.g., a write operation, the modified data is marked “dirty” using thedirty bit 670 so that the inode (block) can be subsequently “flushed”(stored) to disk. The in-core and on-disk format structures of the WAFLfile system, including the inodes and inode file, are disclosed anddescribed in the previously incorporated U.S. Pat. No. 5,819,292 titledMETHOD FOR MAINTAINING CONSISTENT STATES OF A FILE SYSTEM AND FORCREATING USER-ACCESSIBLE READ-ONLY COPIES OF A FILE SYSTEM by David Hitzet al., issued on Oct. 6, 1998.

FIG. 7 is a schematic block diagram of an embodiment of a buffer tree ofa file that may be advantageously used with the present invention. Thebuffer tree is an internal representation of blocks for a file (e.g.,file 700) loaded into the memory 224 and maintained by thewrite-anywhere file system 360. A root (top-level) inode 702, such as anembedded inode, references indirect (e.g., level 1) blocks 704. Notethat there may be additional levels of indirect blocks (e.g., level 2,level 3) depending upon the size of the file. The indirect blocks (andinode) contain pointers 705 that ultimately reference data blocks 706used to store the actual data of the file. That is, the data of file 700are contained in data blocks and the locations of these blocks arestored in the indirect blocks of the file. Each level 1 indirect block704 may contain pointers to as many as 1024 data blocks. According tothe “write anywhere” nature of the file system, these blocks may belocated anywhere on the disks 130.

A file system layout is provided that apportions an underlying physicalvolume into one or more virtual volumes (or flexible volume) of astorage system, such as node 200. An example of such a file systemlayout is described in U.S. patent application Ser. No. 10/836,817titled EXTENSION OF WRITE ANYWHERE FILE SYSTEM LAYOUT, by John K.Edwards et al. and assigned to Network Appliance, Inc. The underlyingphysical volume is an aggregate comprising one or more groups of disks,such as RAID groups, of the node. The aggregate has its own physicalvolume block number (pvbn) space and maintains meta-data, such as blockallocation structures, within that pvbn space. Each flexible volume hasits own virtual volume block number (vvbn) space and maintainsmeta-data, such as block allocation structures, within that vvbn space.Each flexible volume is a file system that is associated with acontainer file; the container file is a file in the aggregate thatcontains all blocks used by the flexible volume. More-over, eachflexible volume comprises data blocks and indirect blocks that containblock pointers that point at either other indirect blocks or datablocks.

In one embodiment, pvbns are used as block pointers within buffer treesof files (such as file 700) stored in a flexible volume. This “hybrid”flexible volume embodiment involves the insertion of only the pvbn inthe parent indirect block (e.g., inode or indirect block). On a readpath of a logical volume, a “logical” volume (vol) info block has one ormore pointers that reference one or more fsinfo blocks, each of which,in turn, points to an inode file and its corresponding inode buffertree. The read path on a flexible volume is generally the same,following pvbns (instead of vvbns) to find appropriate locations ofblocks; in this context, the read path (and corresponding readperformance) of a flexible volume is substantially similar to that of aphysical volume. Translation from pvbn-to-disk,dbn occurs at the filesystem/RAID system boundary of the storage operating system 300.

In an illustrative dual vbn hybrid flexible volume embodiment, both apvbn and its corresponding vvbn are inserted in the parent indirectblocks in the buffer tree of a file. That is, the pvbn and vvbn arestored as a pair for each block pointer in most buffer tree structuresthat have pointers to other blocks, e.g., level 1 (L1) indirect blocks,inode file level 0 (L0) blocks. FIG. 8 is a schematic block diagram ofan illustrative embodiment of a buffer tree of a file 800 that may beadvantageously used with the present invention. A root (top-level) inode802, such as an embedded inode, references indirect (e.g., level 1)blocks 804. Note that there may be additional levels of indirect blocks(e.g., level 2, level 3) depending upon the size of the file. Theindirect blocks (and inode) contain pvbn/vvbn pointer pair structures808 that ultimately reference data blocks 806 used to store the actualdata of the file.

The pvbns reference locations on disks of the aggregate, whereas thevvbns reference locations within files of the flexible volume. The useof pvbns as block pointers 808 in the indirect blocks 804 providesefficiencies in the read paths, while the use of vvbn block pointersprovides efficient access to required meta-data. That is, when freeing ablock of a file, the parent indirect block in the file contains readilyavailable vvbn block pointers, which avoids the latency associated withaccessing an owner map to perform pvbn-to-vvbn translations; yet, on theread path, the pvbn is available.

FIG. 9 is a schematic block diagram of an embodiment of an aggregate 900that may be advantageously used with the present invention. Luns(blocks) 902, directories 904, qtrees 906 and files 908 may be containedwithin flexible volumes 910, such as dual vbn flexible volumes, that, inturn, are contained within the aggregate 900. The aggregate 900 isillustratively layered on top of the RAID system, which is representedby at least one RAID plex 950 (depending upon whether the storageconfiguration is mirrored), wherein each plex 950 comprises at least oneRAID group 960. Each RAID group further comprises a plurality of disks930, e.g., one or more data (D) disks and at least one (P) parity disk.

Whereas the aggregate 900 is analogous to a physical volume of aconventional storage system, a flexible volume is analogous to a filewithin that physical volume. That is, the aggregate 900 may include oneor more files, wherein each file contains a flexible volume 910 andwherein the sum of the storage space consumed by the flexible volumes isphysically smaller than (or equal to) the size of the overall physicalvolume. The aggregate utilizes a physical pvbn space that defines astorage space of blocks provided by the disks of the physical volume,while each embedded flexible volume (within a file) utilizes a logicalvvbn space to organize those blocks, e.g., as files. Each vvbn space isan independent set of numbers that corresponds to locations within thefile, which locations are then translated to dbns on disks. Since theflexible volume 910 is also a logical volume, it has its own blockallocation structures (e.g., active, space and summary maps) in its vvbnspace.

A container file is a file in the aggregate that contains all blocksused by a flexible volume. The container file is an internal (to theaggregate) feature that supports a flexible volume; illustratively,there is one container file per flexible volume. Similar to a purelogical volume in a file approach, the container file is a hidden file(not accessible to a user) in the aggregate that holds every block inuse by the flexible volume. The aggregate includes an illustrativehidden meta-data root directory that contains subdirectories of flexiblevolumes:WAFL/fsid/filesystem file, storage label file

Specifically, a physical file system (WAFL) directory includes asubdirectory for each flexible volume in the aggregate, with the name ofsubdirectory being a file system identifier (fsid) of the flexiblevolume. Each fsid subdirectory (flexible volume) contains at least twofiles, a filesystem file and a storage label file. The storage labelfile is illustratively a 4 kB file that contains meta-data similar tothat stored in a conventional raid label. In other words, the storagelabel file is the analog of a raid label and, as such, containsinformation about the state of the flexible volume such as, e.g., thename of the flexible volume, a universal unique identifier (uuid) andfsid of the flexible volume, whether it is online, being created orbeing destroyed, etc.

FIG. 10 is a schematic block diagram of an on-disk representation of anaggregate 1000. The storage operating system 300, e.g., the RAID system380, assembles a physical volume of pvbns to create the aggregate 1000,with pvbns 1 and 2 comprising a “physical” volinfo block 1002 for theaggregate. The volinfo block 1002 contains block pointers to fsinfoblocks 1004, each of which may represent a snapshot of the aggregate.Each fsinfo block 1004 includes a block pointer to an inode file 1006that contains inodes of a plurality of files, including an owner map1010, an active map 1012, a summary map 1014 and a space map 1016, aswell as other special meta-data files. The inode file 1006 furtherincludes a root directory 1020 and a “hidden” meta-data root directory1030, the latter of which includes a namespace having files related to aflexible volume in which users cannot “see” the files. The hiddenmeta-data root directory includes the WAFL/fsid/directory structure thatcontains filesystem file 1040 and storage label file 1090. Note thatroot directory 1020 in the aggregate is empty; all files related to theaggregate are organized within the hidden meta-data root directory 1030.

In addition to being embodied as a container file having level 1 blocksorganized as a container map, the filesystem file 1040 includes blockpointers that reference various file systems embodied as flexiblevolumes 1050. The aggregate 1000 maintains these flexible volumes 1050at special reserved inode numbers. Each flexible volume 1050 also hasspecial reserved inode numbers within its flexible volume space that areused for, among other things, the block allocation bitmap structures. Asnoted, the block allocation bitmap structures, e.g., active map 1062,summary map 1064 and space map 1066, are located in each flexiblevolume.

Specifically, each flexible volume 1050 has the same inode filestructure/content as the aggregate, with the exception that there is noowner map and no WAFL/fsid/filesystem file, storage label file directorystructure in a hidden meta-data root directory 1080. To that end, eachflexible volume 1050 has a volinfo block 1052 that points to one or morefsinfo blocks 1054, each of which may represent a snapshot, along withthe active file system of the flexible volume. Each fsinfo block, inturn, points to an inode file 1060 that, as noted, has the same inodestructure/content as the aggregate with the exceptions noted above. Eachflexible volume 1050 has its own inode file 1060 and distinct inodespace with corresponding inode numbers, as well as its own root (fsid)directory 1070 and subdirectories of files that can be exportedseparately from other flexible volumes.

The storage label file 1090 contained within the hidden meta-data rootdirectory 1030 of the aggregate is a small file that functions as ananalog to a conventional raid label. A raid label includes physicalinformation about the storage system, such as the volume name; thatinformation is loaded into the storage label file 1090. Illustratively,the storage label file 1090 includes the name 1092 of the associatedflexible volume 1050, the online/offline status 1094 of the flexiblevolume, and other identity and state information 1096 of the associatedflexible volume (whether it is in the process of being created ordestroyed).

F. VLDB

FIG. 11 is a schematic block diagram illustrating a collection ofmanagement processes that execute as user mode applications 1100 on thestorage operating system 300 to provide management of configurationinformation (i.e. management data) for the nodes of the cluster. To thatend, the management processes include a management framework process1110 and a volume location database (VLDB) process 1130, each utilizinga data replication service (RDB 1150) linked as a library. Themanagement framework 1110 provides a user to an administrator 1170interface via a command line interface (CLI) and/or a web-basedgraphical user interface (GUI). The management framework isillustratively based on a conventional common interface model (CIM)object manager that provides the entity to which users/systemadministrators interact with a node 200 in order to manage the cluster100.

The VLDB 1130 is a database process that tracks the locations of variousstorage components (e.g., SVSs, flexible volumes, aggregates, etc.)within the cluster 100 to thereby facilitate routing of requeststhroughout the cluster. In the illustrative embodiment, the N-blade 310of each node accesses a configuration table 235 that maps the SVS ID 502of a data container handle 500 to a D-blade 350 that “owns” (services)the data container within the cluster. The VLDB includes a plurality ofentries which, in turn, provide the contents of entries in theconfiguration table 235; among other things, these VLDB entries keeptrack of the locations of the flexible volumes (hereinafter generally“volumes 910”) and aggregates 900 within the cluster. Examples of suchVLDB entries include a VLDB volume entry 1200 and a VLDB aggregate entry1300.

FIG. 12 is a schematic block diagram of an exemplary VLDB volume entry1200. The entry 1200 includes a volume ID field 1205, an aggregate IDfield 1210 and, in alternate embodiments, additional fields 1215. Thevolume ID field 1205 contains an ID that identifies a volume 910 used ina volume location process. The aggregate ID field 1210 identifies theaggregate 900 containing the volume identified by the volume ID field1205. Likewise, FIG. 13 is a schematic block diagram of an exemplaryVLDB aggregate entry 1300. The entry 1300 includes an aggregate ID field1305, a D-blade ID field 1310 and, in alternate embodiments, additionalfields 1315. The aggregate ID field 1305 contains an ID of a particularaggregate 900 in the cluster 100. The D-blade ID field 1310 contains anID of the D-blade hosting the particular aggregate identified by theaggregate ID field 1305.

The VLDB illustratively implements a RPC interface, e.g., a Sun RPCinterface, which allows the N-blade 310 to query the VLDB 1130. Whenencountering contents of a data container handle 500 that are not storedin its configuration table, the N-blade sends an RPC to the VLDBprocess. In response, the VLDB 1130 returns to the N-blade theappropriate mapping information, including an ID of the D-blade thatowns the data container. The N-blade caches the information in itsconfiguration table 235 and uses the D-blade ID to forward the incomingrequest to the appropriate data container. All functions andinteractions between the N-blade 310 and D-blade 350 are coordinated ona cluster-wide basis through the collection of management processes andthe RDB library user mode applications 1100.

To that end, the management processes have interfaces to (are closelycoupled to) RDB 1150. The RDB comprises a library that provides apersistent object store (storing of objects) for the management dataprocessed by the management processes. Notably, the RDB 1150 replicatesand synchronizes the management data object store access across allnodes 200 of the cluster 100 to thereby ensure that the RDB databaseimage is identical on all of the nodes 200. At system startup, each node200 records the status/state of its interfaces and IP addresses (thoseIP addresses it “owns”) into the RDB database.

G. Storage System Architecture

The present invention is related to a storage system architectureillustratively comprising two or more volumes 910 distributed across aplurality of nodes 200 of cluster 100. The volumes are organized as aSVS and configured to store content of data containers, such as filesand luns, served by the cluster in response to multi-protocol dataaccess requests issued by clients 180. Notably, the content of each datacontainer is apportioned among the volumes of the SVS to thereby improvethe efficiency of storage service provided by the cluster. To facilitatea description and understanding of the present invention, datacontainers are hereinafter referred to generally as “files”.

According to an aspect of the invention, the SVS comprises a meta-datavolume (MDV) and one or more data volumes (DV). The MDV is configured tostore a canonical copy of meta-data, including access control lists(ACLs) and directories, associated with all files stored on the SVS,whereas each DV is configured to store, at least, data content of thosefiles. For each file stored on the SVS, one volume is designated the CAVand, to that end, is configured to store (“cache”) certain,rapidly-changing attribute meta-data associated with that file tothereby offload access requests that would otherwise be directed to theMDV. In the illustrative embodiment described herein, determination ofthe CAV for a file is based on a simple rule: designate the volumeholding the first stripe of content (data) for the file as the CAV forthe file. Not only is this simple rule convenient, but it also providesan optimization for small files. That is, a CAV may be able to performcertain operations without having to communicate with other volumes ofthe SVS if the file is small enough to fit within the specified stripewidth. Ideally, the first stripes of data for files are distributedamong the DVs of the SVS to thereby facilitate even distribution of CAVdesignations among the volumes of the SVS. In an alternate embodiment,data for files is striped across the MDV and the DVs.

FIG. 14 is a schematic block diagram of the inode files of an SVS 1400in accordance with an embodiment of the present invention. The SVS 1400illustratively comprises three volumes, namely MDV 1405 and two DVs1410, 1415. It should be noted that in alternate embodiments additionaland/or differing numbers of volumes may be utilized in accordance withthe present invention. Illustratively, the MDV 1405 stores a pluralityof inodes, including a root directory (RD) inode 1420, a directory (DIR)inode 1430, file (F) inodes 1425, 1435, 1445 and an ACL inode 1440. Eachof these inodes illustratively includes meta-data (M) associated withthe inode. In the illustrative embodiment, each inode on the MDV 1405does not include data (D); however, in alternate embodiments, the MDVmay include user data.

In contrast, each DV 1410, 1415 stores only file (F) inodes 1425, 1435,1445 and ACL inode 1440. According to the inventive architecture, a DVdoes not store directories or other device inodes/constructs, such assymbolic links; however, each DV does store F inodes, and may storecached copies of ACL inodes, that are arranged in the same locations astheir respective inodes in the MDV 1405. A particular DV may not store acopy of an inode until an I/O request for the data container associatedwith the inode is received by the D-Blade serving a particular DV.Moreover, the contents of the files denoted by these F inodes areperiodically sparse according to SVS striping rules, as describedfurther herein. In addition, since one volume is designated the CAV foreach file stored on the SVS 1400, DV 1415 is designated the CAV for thefile represented by inode 1425 and DV 1410 is the CAV for the filesidentified by inodes 1435, 1445. Accordingly, these CAVs cache certain,rapidly-changing attribute meta-data (M) associated with those filessuch as, e.g., file size 615, as well as access and/or modification timestamps 620.

According to another aspect of the invention, the SVS is associated witha set of striping rules that define a stripe algorithm, a stripe widthand an ordered list of volumes within the SVS. The striping rules foreach SVS are illustratively stored as an entry of VLDB 1130 and accessedby SVS ID. FIG. 15 is a schematic block diagram of an exemplary VLDB SVSentry 1500 in accordance with an embodiment of the present invention.The VLDB entry 1500 includes a SVS ID field 1505 and one or more sets ofstriping rules 1530. In alternate embodiments additional fields 1535 maybe included. The SVS ID field 1505 contains the ID of a SVS which, inoperation, is specified in data container handle 500.

Each set of striping rules 1530 illustratively includes a stripe widthfield 1510, a stripe algorithm ID field 1515, an ordered list of volumesfield 1520 and, in alternate embodiments, additional fields 1525. Thestriping rules 1530 contain information for identifying the organizationof a SVS. For example, the stripe algorithm ID field 1515 identifies astriping algorithm used with the SVS. In the illustrative embodiment,multiple striping algorithms could be used with a SVS; accordingly,stripe algorithm ID is needed to identify which particular algorithm isutilized. Each striping algorithm, in turn, specifies the manner inwhich file content is apportioned as stripes across the plurality ofvolumes of the SVS. The stripe width field 1510 specifies the size/widthof each stripe. The ordered list of volumes field 1520 contains the IDsof the volumes comprising the SVS. In an illustrative embodiment, theordered list of volumes comprises a plurality of tuples comprising of aflexible volume ID and the aggregate ID storing the flexible volume.Moreover, the ordered list of volumes may specify the function andimplementation of the various volumes and striping rules of the SVS. Forexample, the first volume in the ordered list may denote the MDV of theSVS, whereas the ordering of volumes in the list may denote the mannerof implementing a particular striping algorithm, e.g., round-robin.

According to yet another aspect of the invention, a Locate( ) function375 is provided that enables the VSM 370 and other modules (such asthose of N-blade 310) to locate a D-blade 350 and its associated volumeof a SVS 1400 in order to service an access request to a file. TheLocate( ) function takes as arguments, at least (i) a SVS ID 1505, (ii)an offset within the file, (iii) the inode number for the file and (iv)a set of striping rules 1530, and returns the volume 910 on which thatoffset begins within the SVS 1400. For example, assume a data accessrequest directed to a file is issued by a client 180 and received at theN-blade 310 of a node 200, where it is parsed through the multi-protocolengine 325 to the appropriate protocol server of N-blade 310.

To determine the location of a D-blade 350 to which to transmit a CFmessage 400, the N-blade 310 may first retrieve a SVS entry 1500 toacquire the striping rules 1530 (and list of volumes 1520) associatedwith the SVS. The N-blade 310 then executes the Locate( ) function 375to identify the appropriate volume to which to direct an operation.Thereafter, the N-Blade may retrieve the appropriate VLDB volume entry1200 to identify the aggregate containing the volume and the appropriateVLDB aggregate entry 1300 to ultimately identify the appropriate D-blade350. The protocol server of N-blade 310 then transmits the CF message400 to the D-blade 350.

FIG. 16 is a schematic block diagram illustrating the periodicsparseness of file content stored on volumes A 1605, B 1610 and C 1615of SVS 1600 in accordance with an embodiment of the present invention.As noted, file content is periodically sparse according to the SVSstriping rules, which specify a striping algorithm (as indicated bystripe algorithm ID field 1515) and a size/width of each stripe (asindicated by stripe width field 1510). Note that, in the illustrativeembodiment, a stripe width is selected to ensure that each stripe mayaccommodate the actual data (e.g., stored in data blocks 806) referencedby an indirect block (e.g., level 1 block 804) of a file. In accordancewith an illustrative round robin striping algorithm, volume A 1605contains a stripe of file content or data (D) 1620 followed, insequence, by two stripes of sparseness (S) 1622, 1624, another stripe ofdata (D) 1626 and two stripes of sparseness (S) 1628, 1630. Volume B1610, on the other hand, contains a stripe of sparseness (S) 1632followed, in sequence, by a stripe of data (D) 1634, two stripes ofsparseness (S) 1636, 1638, another stripe of data (D) 1640 and a stripeof sparseness (S) 1642. Volume C 1615 continues the round robin stripingpattern and, to that end, contains two stripes of sparseness (S) 1644,1646 followed, in sequence, by a stripe of data (D) 1648, two stripes ofsparseness (S) 1650, 1652 and another stripe of data (D) 1654.

H. SVS Operations

According to the storage system architecture described herein, aplurality of SVS operations are provided to enable efficient andaccurate serving of file (and other data container) content distributedacross volumes of a SVS. These SVS operations include, among others,create file, delete file, retrieve attributes of file, write/modifyattributes of file, read file and write file operations. FIG. 17 is aflowchart detailing the steps of a procedure 1700 for creating a newfile in accordance with an embodiment of the present invention. Theprocedure 1700 begins in step 1705 and continues to step 1710 where anN-blade 310 receives a request to create a new file by, e.g., a client180 sending a create file request to node 200. In step 1715, the N-bladere-directs the request to the appropriate D-blade serving the MDV 1405of a SVS 1400. Illustratively, the N-blade translates the create filerequest to a procedure call (LPC or RPC) and then determines an actionit should take depending upon the CF API function associated with thatcall. For example, in response to a create file request, the N-bladeissues a corresponding create file procedure call to the MDV 1405 or,more specifically, the VSM 370 of the D-blade 350 serving the MDV.

In the illustrative embodiment, the N-blade determines which volume of aSVS 1400 is the MDV by examining the ordered list of volumes 1520 withinthe SVS entry 1500 of the VLDB 1130. As noted, the first volume listedin the ordered list of volumes 1520 is illustratively the MDV, althoughit will be understood to those skilled in the art that any volumeposition within the ordered list can be designated the MDV 1405.Moreover, the VLDB entry 1500 can be augmented to explicitly state whichvolume in the ordered list 1520 is the MDV of the SVS.

Upon receiving the create file procedure call, the VSM 370 processesthat call by updating the directory (i.e., creating a new directoryentry for the file) on the MDV in Step 1718 and, in step 1720,allocating an inode for the file. The allocated inode is preferablyselected from among available inodes in the SVS using, e.g., anyconventional inode selection technique. Note that each volume of the SVS1400 is allocated the same inode for the newly created file. Moreover,the inode is allocated in the same position/location of the inode filefor each volume, i.e., the file inode on each volume is allocated thesame inode index to the inode file. In step 1735, the VSM 370 of the MDV1405 completes file creation by, e.g., instructing the file system 360operating on the D-blade 350 to create a file using the allocated inode.The procedure 1700 then completes in step 1740.

FIG. 18 is a flowchart detailing the steps of a procedure 1800 fordeleting a file in accordance with an embodiment of the presentinvention. The procedure 1800 begins in step 1805 and continues to step1810 where an N-blade receives a client request to delete a file. Instep 1815, the N-blade re-directs the request as a delete file procedurecall to the VSM 370 of the appropriate D-blade serving the MDV 1405 of aSVS 1400, as described herein. In step 1825, the VSM passes acorresponding delete request to the file system 360 via, e.g., aconventional IPC mechanism such as issuing a procedure call or passing amessage. In step 1830, the file system processes the delete (deletion)request up to the point of actually removing the inode from the filesystem. At this point, the file system alerts the VSM 370 that it hasreached this particular state (step 1835) via, e.g., the IPC mechanism.In step 1840, the VSM sends requests to all DVs in the SVS to free thestorage associated with the inode. Illustratively, the VSM 370 sendsthese requests as CF messages 400 in cooperation with the CF interfacemodules 340 of the D-blades serving the DVs of the SVS 1400. Then, instep 1842, the CSM waits until all of the DVs have acknowledgedcompletion of the request. In step 1845, the VSM instructs the filesystem 360 to delete the inode and, in response, the file system deletesthe inode in step 1850. The procedure then completes in step 1855.

FIG. 19 is a flowchart detailing the steps of a procedure 1900 forretrieving attributes of a file in accordance with an embodiment of thepresent invention. The procedure 1900 begins in step 1905 and continuesto step 1910 where an N-blade receives a request to retrieve (read) fileattributes. In step 1915, the N-blade forwards the request to the VSM ofthe D-blade hosting the CAV of the file. In step 1920, the VSM 370determines whether its cached copy of the meta-data attributes is valid,i.e., has been invalidated, by checking the meta-data invalidation flag634 of the inode 600 of the file. If the cached copy has not beeninvalidated, the VSM returns the requested attributes in step 1930 andthe procedure completes in step 1935. However, if the cached copy hasbeen invalidated, the procedure branches to step 1925 where the VSMretrieves the attributes from the MDV 1405 by, e.g., sending anattribute retrieval request to the D-blade 350 serving the MDV.Illustratively, such a request is sent as a CF message 400 via the CFinterface modules 340. The procedure then continues to step 1930 wherethe VSM of the D-blade hosting the CAV returns the requested attributesbefore completing in step 1935.

FIG. 20 is a flowchart detailing the steps of a procedure 2000 forwriting/modifying file attributes in accordance with an embodiment ofthe present invention. The procedure 2000 begins in step 2005 andcontinues to step 2010 where an N-blade receives a request to modifyfile attributes. In step 2015, the N-blade forwards the request to theVSM 370 of the D-blade 350 hosting the MDV. The VSM serving the MDVthen, in step 2020, forwards a request to invalidate its cached copy ofmeta-data to the VSM serving the CAV of the file. In response, the VSMof the CAV invalidates it cache in step 2025 by, for example, settingthe meta-data invalidation flag 634 to signify that its cached meta-datais not valid. The VSM serving the CAV also forwards the invalidationrequest to all DVs and waits until it has received a response from eachVSM before then acknowledging that it has invalidated its cache in step2030. Once the VSM serving the MDV receives this acknowledgement, itmodifies the canonical copy of the meta-data per the received request tomodify file attributes (step 2035). The VSM then returns a statusindicator, e.g., indicating that the operation was successful, to theN-Blade in step 2040, before the N-Blade responds to the client with astatus in step 2045. The procedure then completes step 2050.

FIG. 21 is a flowchart detailing the steps of a procedure 2100 forprocessing a read request in accordance with an embodiment of thepresent invention. The procedure 2100 begins in step 2105 and continuesto step 2110 where an N-blade receives the read request from a client.In step 2115, the N-blade utilizes the Locate( ) function 375 toidentify the D-blade to which to re-direct the request. As noted above,the Locate( ) function takes as arguments a SVS ID, a set of stripingrules, an inode number and an offset into the file, and returns theidentity (ID) of the appropriate volume that serve the file offset. Instep 2120, the N-blade forwards the request to the appropriate D-blade350, where the VSM 370 determines if the read request will fit onto asingle stripe on the volume, i.e., whether the read request is for datathat is entirely contained within a stripe on this volume. If so, thenthe VSM 370 illustratively performs a series of checks to determinewhether it may immediately process the request.

For example, the VSM determines whether its local cached copy of certainmeta-data exists (step 2125), whether the read request is less than thecached file length (step 2130) and whether the CAV for the file has beenconsulted recently (step 2135). Collectively, these checks ensure thatthe CAV has relatively recently checked the appropriate meta-data forthe file. If any of these checks are answered in the negative, theprocedure branches to step 2140 where the VSM of the CAV updates itslocally cached copy of the file meta-data by, e.g., querying the MDV forthe most up-to-date meta-data. However, if the checks are positivelysatisfied, the procedure proceeds to step 2145 where the VSM passes theread request to the file system. In step 2150, the file system processesthe read request by, e.g., retrieving the appropriate data from disk. Instep 2155, the file system returns a response to the N-blade which, instep 2160, returns the appropriate response to the client. This responseincludes, e.g., the requested read data from the volume and also anyrequested data retrieved from other volumes as described further below.The procedure then completes in step 2165.

However, if in step 2122 a determination is made that the requested readdata does not entirely fit onto the stripe, the procedure branches tostep 2170 where the VSM passes a read request for the data that does notfit onto this stripe to the VSM of the volume serving the next stripe ofdata. In response, the VSM of the volume holding the next stripe of dataservices the read request and returns the requested data to therequesting VSM in step 2175. The procedure then continues to step 2125.

FIG. 22 is a flowchart detailing the steps of a procedure 2200 forprocessing a write request in accordance with an embodiment of thepresent invention. The procedure 2200 begins in step 2202 and continuesto step 2205 where an N-blade receives the write request from a client.In step 2210, the N-blade illustratively utilizes the Locate( ) function375, as described herein, to identify the D-blade to which to re-directthe request for processing. In step 2215, the N-blade forwards therequest to the appropriate D-blade(s). In step 2220, the VSM on theD-blade determines whether the data to be written fits into a singlestripe. Illustratively, the VSM may compute this determination byanalyzing the size of the write operation, the stripe width and theoffset within the stripe where the write operation begins.

If the write fits within a single stripe, the VSM performs the threechecks described above with respect to a read operation, namelydetermining whether a local cache is ready for use (step 2225), whetherthe write request is less than the cached file length (step 2230) andwhether the FAV has been consulted recently (step 2235). If any of thesechecks fail, the procedure branches to step 2255 where the VSM retrievesthe meta-data from the CAV and onto step 2240. However, if the answersto all the checks are positive, the procedure continues directly to step2240 where the VSM passes the write request to the file system. In step2245, the file system processes the write request before returning astatus to the N-blade in step 2250. The procedure then completes in step2290.

In step 2270, the VSM passes a portion of the data associated with thewrite operation to its file system 360 360, which writes that portion ofthe data to its volume in step 2275. In step 2280, the VSM passes theexcess data associated with the write operation to the volume in the SVSconfigured to store a next stripe. In step 2285, the VSM for that volumepasses the excess data to its file system for writing (storing) on thevolume. Thereafter, in step 2250, the file system returns a status tothe N-blade and the procedure completes in step 2290.

The foregoing description has been directed to particular embodiments ofthis invention. It will be apparent, however, that other variations andmodifications may be made to the described embodiments, with theattainment of some or all of their advantages. Specifically, it shouldbe noted that the principles of the present invention may be implementedin non-distributed file systems. Furthermore, while this description hasbeen written in terms of N and D-blades, the teachings of the presentinvention are equally suitable to systems where the functionality of theN and D-blades are implemented in a single system. Alternately, thefunctions of the N and D-blades may be distributed among any number ofseparate systems, wherein each system performs one or more of thefunctions. Additionally, the procedures, processes and/or modulesdescribed herein may be implemented in hardware, software, embodied as acomputer-readable medium having program instructions, firmware, or acombination thereof. Therefore, it is the object of the appended claimsto cover all such variations and modifications as come within the truespirit and scope of the invention.

1. A system for striping one or more data containers across a stripedvolume set, the system comprising of: a plurality of volumes organizedinto the striped volume set, the striped volume set defined by a set ofstriping rules; and a volume striping module executing on one or morecomputers in a cluster, each of the computers serving one or more of theplurality of volumes, wherein the volume striping module implementscommands directed to the striped volume set.
 2. The system of claim 1wherein the set of file striping rules comprises a stripe width.
 3. Thesystem of claim 1 wherein the striping rules comprises a stripingalgorithm identifier that identifies a striping algorithm utilized withthe striped volume set.
 4. The system of claim 1 wherein the stripingrules comprises an ordered set of volumes.
 5. The system of claim 4wherein a first of the ordered set of volumes comprises a meta-datavolume.
 6. The system of claim 1 wherein one of the plurality of volumesis defined as a container attribute volume for each of the one or moredata containers striped across the striped volume set.
 7. A system forstriping one or more data containers across a striped volume set, thesystem comprising: one or more network elements adapted to receivecommands from a client directed to the striped volume set and furtheradapted to translate the received commands into a protocol forcommunication with one of one or more disk elements; wherein each of thedisk elements comprises a volume striping module adapted to process theprotocol to implement operations directed to the striped volume set. 8.The system of claim 7 wherein the striped volume set comprises of aplurality of volumes, each of the plurality of volumes being served byone of the one or more disk elements.
 9. The system of claim 7 whereinthe striped volume set is defined by a set striping rules.
 10. Thesystem of claim 9 wherein the set of striping rules comprises a stripewidth.
 11. The system of claim 9 wherein the striping rules comprises astriping algorithm indicator, the striping algorithm indicatoridentifying a striping algorithm utilized with the striped volume set.12. The system of claim 9 wherein the striping rules comprises anordered set of volumes.
 13. The system of claim 9 wherein a first of theordered set of volumes comprises a meta-data volume.
 14. A method forstriping one or more data containers across a striped volume set, themethod comprising the steps of: defining the striped volume set using aset of striping rules; organizing a plurality of volumes organized intothe striped volume set, the striped volume set defined by a set ofstriping rules; and providing a volume striping module executing on oneor more computers in a cluster, each of the computers serving one ormore of the plurality of volumes, wherein the volume striping moduleimplements commands directed to the striped volume set.
 15. The methodof claim 14 wherein the set of striping rules comprises a stripe width.16. The method of claim 14 wherein the striping rules comprises astriping algorithm identifier that identifies a striping algorithmutilized with the striped volume set.
 17. The method of claim 14 whereinthe striping rules comprises an ordered set of volumes.
 18. The methodof claim 17 wherein a first of the ordered set of volumes comprises ameta-data volume.
 19. The method of claim 14 further comprising the stepof defining one of the plurality of volumes as a container attributevolume for each of the one or more data containers striped across thestriped volume set.
 20. The method of claim 14 further comprising thestep of defining one of the plurality of volumes as a meta-data volume.